Non-Covalent Functionalized Tetraphenylporphyrin Derivatives/Chemically Reduced Graphene Oxide Nanosensors for the Electrochemical Detection of Nitrobenzene

Abstract

Terrorism has become a serious threat to the public security across the globe in the recent years. It has become an issue of utmost importance. Private citizens, states and nations have to play their role in strategic vision in order to prepare, recognize and prevent such violence. Due to increased terrorist attacks, it is the demand of era to develop some highly portable, sensitive and miniaturized devices for the detection of such explosive materials. Nitroaromatic compounds are widely used for military munitions especially as major component of explosive materials. Nitrobenzene is chemically and structurally similar to these explosives. A number of approaches have been adopted to detect nitrobenzene. These approaches include reverse-phase HPLC, surface enhanced Raman scattering, immunosensing, chemiluminescence spectrophotometry and electrochemical method. One method that offers a possible route for the development of sensing system is the use of functionalized graphene based nanosensors. I have synthesized graphene oxide, reduced graphene oxide and pristine graphene by Hummers’ method, chemical reduction method and liquid phase exfoliation of graphite. Tetraphenylporphyrin (TPP), 5,10,15,20-tetrakis(4-chlorophenyl)porphyrin (Cl4 TPP) were prepared by Adler-Longo method while copper tetraphenylporphyrin (Cu-TPP), copper 5,10,15,20-tetrakis(4- chlorophenyl)porphyrin were prepared by simple metalation of TPP and Cl4 TPP. The graphene based nanomaterials were functionalized with tetraphenylporphyrin, copper tetraphenylporphyrin, 5,10,15,20-tetrakis(4-chlorophenyl)porphyrin and copper 5,10,15,20-tetrakis(4- chlorophenyl)porphyrin. PGr-TPP, PGr-Cu TPP, RGO-TPP, RGO-Cu TPP, PGr-Cl4 TPP, PGr-Cu Cl4 TPP, RGO-Cl4 TPP, RGO-Cu Cl4 TPP nanocomposites were prepared in 1:0.5, 1:1 and 1:2 ratios to detect nitrobenzene as analyte. The synthesized compounds GO, RGO, PGr, TPP, Cu TPP, Cl4 Tpp and Cu Cl4 TPP were characterized by Nuclear Magnetic Spectroscopy (NMR), Scanning Electron Microscopy (SEM), Infrared and UV-vis spectroscopy. The electrochemical sensing properties of nanocomposites were evaluated by using electrochemical impedance spectroscopy and cyclic voltammetry. Porphyrin based graphene nanocomposite shows high sensitivity, selectivity and reproducibility for nitrobenzene. Among all the nanocomposites, RGO-Cu Cl4 TPP in 1:2 shows high peak current, least charge transfer resistance and limit of detection (LOD) was determined to be 0.07 mM. The electrochemical sensing properties of graphene based nanocomposites are attributed to the best adsorptive properties, rich electronic system and large electronically active surface area.